Compressor plant



July 21, 1953 R. MUNCK AF ROSENSCHGLD 2,646,205

COMPRESSOR PLANT 3 Sheets-Sheet 1 Filed Aug. 6, 194'? :3: m :33 us;

F VA Jum July 21, 1953 J. R. MUNCK AF ROSENSCHOLD 2,646,205

COMPRESSOR PLANT 5 Sheets-Sheet 2 Filed Aug. 6, 1947 E mm JwO USE.

July 21, 1953 J. R MUNCK AF ROSE NSCHOLD 2,646,205

COMPRESSOR PLANT Filed Aug. 6. 1947 5 SheetsSheet 5 I J M g Y:

RELAY 1, 29

TIME DELAY Patented July 21, 19 53 5 1 UNITED, STATE s PATENT OFFICE,

COMPRESSOR/PLANT John Rutger Munck af Rosenschiild, Saltsjobaden,Sweden, assignor to Aktiebolaget Atlas Diesel, Sickla, near Stockholm,Sweden, a corporation of Sweden 1 Application August 6, 1947, SerialNo.1766,511

In Sweden February. 3, 1942 Section 1, Public Law 690; August 8, 1946Patent expires February 3, 1962 1 asynchronous or auto-sychronous motorswhich between full load and idle speed operate at a constant or nearlyconstant number of revolutions. I

The regulation of the air quantity delivered by such compressors isusually obtained by unloading the compressor in one or more stages. Forthis purpose several known methods may be applied, such as throttling ofthe suction conduit, adding auxiliary clearance spaces to the com.-pression chambers, keeping the suction valves open, and so on. All thesemethods have the disadvantage that the compression is carried out withreduced efiiciency when the compressor is unloaded. This'is usuallyexpressedby'stating that the specific power consumption of thecompressor increases the more the compressor is un-" loaded. v I

, One object of this invention is to providea compressor plant which'op'erates with increased efliciency at'reduced load.

7 Claims. (01.230-44) "Fig. 1 -is a, diagrammatic view showing anelectrically" driven compressor plant and a control circuit thereforeconstructed in accordance with this invention;

"Fig. 2, a view similar to Fig. 1 showing a modiiied compressor driveand "Fig. 3; a view similar to Fig. 1 showing a still further 'modifiedcompressor drive utilizing a change speed-transmission.

. In Fig; 1 a three-phase'short-circuit'motor M ISCOll-l'lBGllGddirectly to an air compressor K,

which delivers compressed airthrough a conduit I8 to a receiver -Bforming part of a compressed The present invention consists of acompres-' sor plant comprising in combination a compressor, anelectromotor for driving said compressor at different numbers ofrevolutions and at d1ffer-- ent loads, means for varying the number ofrevolutions at which the compressor is driven, a mechanism for unloadingthe compressor, a regulating the compressor. The means for varying thenum-.

ber of revolutions of the compressor may be me- {40 -whi'ch'inay be atwo speed pole change asynchanical speed shift gears and/or means forelec- 'trically changing the connections of the motor for driving thecompressor with different numbers of revolutions. The regulating devicemay be-responsive to changes in pressure or temperature of the plant. 7I

In a preferred embodiment the motor, may be connected foroperation withdifferent pole numbers under the influence of the regulating device.

These embodiments of the invention which of the compressed mediumproduced by the plant or any other medium responsive to the operation beclosed by energization of a solenoid 23. -main"switch 'Oi'isconnected toa pole changing air distribution system. The receiver is connected witha control means comprising two electric pressure switches 'Ti and T2by-pipes l, 8. 'Thepressure switch T1, breaks its contact at a pressureP in the receiver B and T at a lowerv pressure p. Furthermore, thereceiver B is connected-to a compressed air relay S by a pipe 9. Saidrelay consists of a valvemember H which by a return force such asaspring not shown' 'is normally kept in the lower one of two positions.

In said normal position, which is illustrated in thedrawing,-pipe 9is'closed while there'is an open-communication between a passage [Ileading-to the atmosphere and a pipe 12 leadingto an unloading mechanism13 on the compressor.

ThereIay Sis operated electromagnetically by' means ofthes'olenoid'lllwhich when energized causes the valve memberluto move tothe upper position in which the communication from the pipe IZ-tothepassage. I l is closed and a communication between the pipes 9 and I2opened; I Three-phase current is supplied to the plant from a line 20and control current from an auxiliary line 2 I. a

, An electrically operated main switch 01 of standard design is providedthrough which the three-phasecurrent is supplied to the motor M,

ch'ronous motor; as soon as a control circuit for the switch'is closed.For this purpose the switch 01 'mayinclude three phase switch means 22which is urged toward the off position by the force of gravity'orothers'uitable'means and which may The switchOz through leads 24, switch02 including switch means 25 which by the force of gravity or 7 othersuitablemeans is urged towardlowposition andwhich may be moved to highposition should only be considered as examples are'described hereinafterwith reference to the accompanying diagrammatic drawings-in which:

by. energization of a solenoid 26. In low position switch means 25connects leads 24 through leads 21 totne low speed'windingof the motor Mand in high position connects leads 24 through leads 28 to the highspeed windings of motor M. This change of connections takes placeaccording to principles known per se, the stator winding of the motorconsisting either of one single winding capable of being connected indififerent ways or of two 01 more diirerent windings. In the illustratedembodiment it is assumedthat the change of connections may be carriedout so that two difierent pole numbersare obtained, of which one istwice the other. Furthermore, it'is assumed that the pole changingswitch 02 normally takes the low position corresponding to the high polenumber when the pertaining control circuit is broken and the highposition corresponding to the low pole number when said circuit isclosed.

The pressure switch T1 controls a circuit containing the solenoid 29 ofa relay R1 and the control circuit of the main switch 01 which runs fromthe line 2i through switch 03, leads 30 and 3|, solenoid 29 of relay R1,lead32, solenoid 23 of switch 01 and lead 33 and 34 to switch 03 'cuitis closed the switch is assumed to take its on position. The relay R1normally closes two contacts I, 2 and when the solenoid 23 is energizedthe contacts are broken with atime delay sufficient to allow motor M toaccelerate the compressor K from rest to low speed. This time delay isof the order of approximately ten seconds.

The contacts l, 2 form a part of the control circuit of the compressedair relay S. This control circuit runs from line 2! through switch 03,leads and 3|, resistance 35, contacts I and 2 of relay R1, solenoid l9and leads 33 and 34 to switch 03 and line 2 I The pressure switch T2controls a circuit from line 2| through switch 03 and leads 3|] and 36to solenoid 3"! of a relay R2, lead 38 and solenoid is of theelectrically operated valve S and leads 33 and 34 to switchOs and line2|. Normally the relay R2 in deenergized state keeps two contacts 3, 4open and closes them with a time delay when the solenoid 31 isenergized. The contacts 3, 4 control a circuit from line 2| throughswitch 03 and leads 34 and 39 to solenoid 4B of relay R3, solenoid 2 5of switch 02 and leads 3!; and so to switch 03 and line 2!. The contacts5, 8 of relay R3 are normally open but close with time delay when thesolenoid 4B is energized.

The contacts 5, 8 of relay R3 are connected in parallel with thesolenoid IQ of the valve S and short-circuit said solenoid l9 when thesole- 7 a The unloading mechanism l3 may in a manner known per seconsist of a piston which under the influence of the compressed air inthe pipe I! and against a spring action lifts the, suction .Yalve orvalves from their seats so that said valve cannot close during thepressure stroke of the compressor piston and the air in the compressorcylinder flows out again through the suction valve. Thus during theoperation of the compressor the air alternately flows out and in throughthe suction valve and no compression work is carried out. In other Wordsthe compressor is unloaded as soon as compressed air is admitted to thepipe [2. On the other hand, if compressed air is conducted away from thepipe 12, the piston of the mechanism It will be returned by the springaction so that the suction valve again takes its normal position and thecompressor is rendered operative.

The compressor plant works in the following manner: If the compressor isat rest and the receiver B contains air of a pressure lower than thepressure at which the pressure switches T1 and T2 break their contactsthe compressor may be started by closing the switch 03. The circuits ofthe pressure switches T1 and T are immediately closed so that the mainswitch 01 is immediately turned on. The motor starts and increases itsspeed to the low number of revolutions corresponding to the highpolenumber which is normally connected by the switch 02 in the low positionshown in Fig. 1. It will be obvious that the motor lvi is at this timesupplied with full line voltage. The solenoid iii of the valve S wasimmediately energized via the contacts 5,2 and the valve was therebymoved to. a position in which the unloading pipe 12 is connected withthe receiver B through the pipe 9 so that the compressor is unloaded.After a time sufficient to accelerate motor M-to low speed andcorresponding to the abovementioned time delay the relay R1 breaks itscontacts I, 2 whereupon, however, the solenoid IQ of the valve S is keptenergized since current is supplied via the switch T2 and the solenoid31- of relay R2. The relay R2 closes its contacts 3, il after the timedelay period so that the pole changing switch 02 is switched over fromthe high to the low polenumber or high speed connections to the motorwhich'oonsequently immediately starts to increase its speed. It will beobvious that the motor M is likewise at this time supplied with fullline voltage. The solenoid 2d of relay R3 is energized upon closure ofcontacts 3 and s of relay R2 and after the time delay period, durinwhich the acceleration of motor M takes place, closes contacts 5 and 6causing the solenoid E9 of the valve Sto be short-circuited'and thevalve S to return to'it's normal position in which the air in theunloading pipe i2 is exhausted so that thecompressor is loaded. Themotor and compressor now have reached full speed and the compressorstarts to pump air into the receiver B in which the pressure rises.

When the pressure has reached the first pressure limit p the pressureswitch T2 is turned off. The solenoid 3'! of relay R2 becomesdeenergized and breaks the control circuit of the pole changing switch02 so that the switch means 25 moves to low position and the motor M isconnected to a high pole number or low speed winding. Also'the solenoidlii oi'the relay R3 is deenergized so that the short-circuit of thesolenoid IS-of the valvesbythe contacts 5, 3 is removed. .The solenoidi9 of the valve S, however, remains deenergizedsince thepressure switchT2 is open. The compressor then operates at about half speed and pumpsair into the receiver at a slower rate.

Now, if the pressure rises tothe upper pressure limit? the pressureswitch T1 also breaks its contacts and the-solenoid 23 1s.deenerg'i'zedso that the main switch 01 controlled therebytdisconnectsthe motor and stops the compressor, the-contacts I, 2are'c1osed andtheysolenoid' l9 of the valve Sis energized and the compressor unloaded.I

was assumed that'this condition lasts until th'e pressure in' thereceiver has fallen belowthe upper pressure limit P, at which time the.pressure switch T1 is again turned on. -The--control-circuit of the mainswitchOiisclosed and: the motor is started and runs up to the-low.number of revolutions since the switch 02 is in low position.

At first the contacts I, 2 are closedandthe solenoid' H) of the valve, Senergized' so that the compressorremainsunloaded via-t-he-pipe} l2.After the time delay period of the relay R1 the itingdevices may:consist of constructions that jduringthe beginning of anew runningperiod of the motor connect'the statorwinding inistar connection andonly after some time change it'over to'mesh connection. *Further thevoltage on the motor at the moment when the connectionis changed: may bereduced by changing the-connectiorr of" variable tapping. points .at: atransformer; said tapping points-being then connected for .normalvoltage in: one. or: more steps. Also current limiting 'impedances or.resistances --m'ay beused for this purposeas shown at 4 lin Fig. 1.

The unloading mechanism 1 3 described-hereinabove may 'be replacedby'athrottle valvein the contacts 1, 2 are broken and-the valve S moved sothat the unloading pipe 12 is connected with the outlet passage ll andthe compressor starts to work. y- I If, however, more compressed air isdrawn from the, receiver B then the supply. from the slowrunningcompressorthe'pressure will fall further and finally passes the lowlimit value 10'. The pressure switch T2 then closes its contacts, thesolenoid 37 of relay R2 and solenoid l9 of valve S become energized, theunloading-pipe I2 is connectedto the pipe 9, andthecompressorsis-unloaded. After the time delay periodof the relay R2 thecontacts 3 and 4 close so that thepole changing switch Q2 is switchedover to highposition and the motor runs with lowpole number andincreases its speed. After-the time delay period of relay R3 this relayalso closes its contacts and short-circuits the solenoid 19 of 'thevalve S so that the compressor is again loaded.

The motor now runs at fullspeed and the compressor works with maximumcapacity.

A plant according to the invention has several important advantages.Firstly, instead of a reduced efiiciency an imp-roved e'fiiciency isobtainedat' half-load at the low' speed. A low specific powerconsumption is obtained since the air velocities in the valves andpassages for the compressor. at the low speed are reduced to about thanin conventional ,plants having devices for reduction of the capacity,'of' the compressor. A

great advantage ist-hatthe starting current of:

the motor also in 'automatic'plants is reduced causingth'e 'motor 'tostart at a? lowsp'eed where its maximum output is less than'half'theoutput at the high speed. Sincethe'value of the startairinlet passage ofthe compressor which 'chokes .sa'id passage when the compressor is to beunloaded.

. In: order not to wear the switches. Or and. O2 unnecessarily byfrequent changes of the con-nections it-:maybe suitable =to' design :thepressure switches. Tr and-Tawith-a certain .inertia or hysteresis.Thismeans for-instance that a rising pressure causes a change-of theconnections inthe direction towards'reduc'ed speed only when the:pressure has: risen. to 'P+D andp-l-d, re-

spectively; where D and dare certain small: pressure differences while:a falling pressure causes a change of'the connections 'in' the directiontowards increased speed, only-when the pressure has fallen to P-D and pd, respectively.

Thepressure switches '-I1= and T2 may be replaced .byanother regulatingdeviceswithman equivalentfunction which upon actuationunder half thevelocities at full speed and a more isothermic compression isobtained'due to better. cooling; The wear of'the moving parts" and theconsumption of lubricant is also more favorable ing current oftenprevents 'the'use of the economical "arrangement with automatidstart andstop; the invention now makes it possible to use.

large compressors'in such an arrangement. I

, The embodiment of the invention hereinabove described and illustratedin Fig. lis only an' example and may be modified in manyways within vthe scope of'the claims.

When a change from stop to runningand from running at low speed torunning'atlhigh speed-=is made i. e. generally speaking,-upon increaseof 'speed,- a"heavy current flow takes place. The

'main switch 01- aswell ,as' the pole changing switch 02 may thereforebe provided with current limiting devices known per 'se' which are'automatically connected during, apcerta'in. period.

This period shouldbe suitably relatedztothe time 'nelay of the relays R1.and R3. wi-The current-limdating purposes. works togetherrwith arefrigerating plant-the reduction in the temperature, for instance in:the refrigeratingspace, below a'certaifi limit may the influence of thecompressed airme'chanic'ally or through fluid pressure "means actuatesthe switches 01 and Oz.

sage immediately after the compressor-the device .may be suchthatwhen'the temperature of the compressed ail" exceeds a certain valueorcertain values, respectively, the change in the connectionspreviouslymentioned is effected.

Furthermore, sincethe compressor consumes more andmore power when the.pressure rises this circumstance,- which is indirectly dependent on thepressure, may be utilized instead of the air. pressure itself.Consequently, a relay responsive to the output of the motor and providedin the supply circuit of the motor may be utilized to actuate theswitches 01 and 02 so that an increase of the output of the motor beyonda certain limit causes a change to'the low speed, whereas a. reductionof'the output below a certain other value m'aycause a change'to the highspeed. In similar manner a device may act which is actuated when theturning moment transmitted from the motor to the-compressor which isindirectly dependent on the air pressure exceeds or falls below acertain value.

Still-further secondary conditions responsive to'the compressor work maybe utilized for regu- For-instance, if the compressor I-Iereinabove, ithas been assumed that one electric motor capable of being connected 'fordifferent speeds is used. However, there is nothing to prevent that, forinstance, two motors are directly coupled to the compressor and thateach motoris designed for a single speed difiering from the speed of theother motor. Both motors may then be of standard design and areconnected alternately by a switch while the motor which is not connectedis carried along idle.

This gives great liberty with regard to the speed relation and also withregard to the number. of speeds, which may be more than two if severalmotors are used. The motors may also be arranged for alternatingseparate operation and operation'in cascade connection providing greatliberty with regard to speed.

Furthermore, different-motors M1 and M2 with the same or differentnormal speeds may be used and arranged to drive the compressor over geartransmissions, as illustrated in Fig. 2, in which gears l4, [5 withdifferent diameters engage a gear wheel 16 fixed n the driven shaft ofthe compressor K. These motors may be connected alternately by theswitch 04 over a suitable coupling mechanism II. The switch 04 andcoupling mechanism [1 then replaces the switch 02 of Fig. 1 whereas theother details of Fig. 2 may be the same and are similarly designated asin Fig. l and are consequently not described again. The change speedswitch 04 includes a switch means .42 which normally connects the lead24 to leads 43 and the motor M1 which through gears l4 and I6 drives thecompressor K at low speed. The switch 04 also includes a solenoid M inseries with solenoid M] of relay R3 and a solenoid 45 which uponenergization shifts mechanism H to a position uncoupling motor M1 andcoupling motor M2 through gears l and Hi to drive compressor K at highspeed. Upon energization. of solenoids 40, 44' and 45 the switch means42 operates to connect the leads M to the leads 46 of motor M2 to drivethe compressor K at high speed. Fig. 3 illustrates a plant of the samegeneral arrangement as in Fig. 1 but having the pole changing switch 02and the motor M replaced by'a speed change. gear 47 and a conventionalmotor M3 adapted to run at one speed only. In

this case the leads 24 from the main switch 01 are connected directlyto' the motor Ms. A solenoid 48 is connected in series with solenoid 40of relay R3 andupon energization shifts the mech-' anism 49 of speedchange gear 41 to drive the compressor K at high speed. V

In certain installations it is often desirable to provide means forlimiting the current flow through the driving motor at the startgradually increasing this current as the speed increases from zero tosome predetermined running speed.

One method for providing such a current limiting control is illustrateddiagrammatically in Fig. l

in which the main switch 01 is provided with a variable resistancedisposed in each power lead 24, the switch arm 22 gradually reducing theresistance in the line as the speed of the driving motor increases.Various devices of this nature are commercially available and anydesired type may be utilizedin the compressor plant of this invention,the showing and description being by way of illustration only.

What I claim is:

1; A compressor plant comprising in combination a compressor electricmotor driving means coupled to said compressor for selectively drivingthe same at diiferent work producing speeds,

said compressor for loading or unloading said compressor and controlmeans operatively associated with the-output of said compressorand'electrically' connected with said speed changing means and with saidunloading mechanism in such a manner that the speed of said compressoris changed in response to a change of a condition resulting from thecompression work of said compressor and that said unloading mechanism isactuated to unload said compressor while the speed thereof is beingincreased from one of said speeds to another.

2. A compressor plant comprising in combination a compressor,multi-speed electric motor driving means coupled to said compressor forselectively driving the same at different work producing speeds, meanssupplying substantially constant voltage to said motor driving means atall work producing speeds, switch means for selecting any one of saidspeeds for operating said compressor to produce compression work whilesaid voltage remains substantially constant, switch actuating means foroperating said switch, unloading mechanism operatively associated withsaid compressor for loading or unloading said compressor and controlmeans operatively associated with the output of said compressor andconnected with said switch actuating means and with said unloadingmechanism in such a manner that the speed of said motor is changed in"response to a change of a condition resulting from the compression workof said compressor and that said unloading mechanism is actuated tounload said compressor while the speed thereof is being increased fromone of said speeds to another.

3. A compressor plant comprising in com-bination a compressor,multi-speed electric motor driving means coupled to said compressor forselectively driving the same at difierent work producing speeds, saiddriving means including an electric motor having a plurality of groupsof poles with a different number of poles in each group which may beselectively energized to operate said motor at different speeds, meansfor supplying substantially constant voltage to said motor driving meansat all work producing speeds, switch means for selecting any one of saidpole groups to thereby change the driving speed for operating saidcompressor to produce compression work while said voltage remains substantially constant, switch actuating'means for operating said switch,unloading mechanism operatively associated with said compressor forloading or unloading said compressor and control means operativelyassociated with the output of said compressor and connected with saidswitch actuating means and with said unloading mechanism in such amanner that the speed of said motor is changed in response to a changeof a condition resulting from the compression work of said compressorand that said unloading mech- U anism is actuated to unload saidcompressor while the speed thereof is being increased one of said speedsto another.

4. A compressor plant as defined in claim 1 in which said speed changingmeans comprises a change speed transmission coupling said motor to saidcompressorfor selectively driving the same at difierent workprodu-cingspeeds and transmission actuating. means for changing thespeed in which said control means includes pressure responsive meansconnected to the output of said compressor, and electrically connectedwith said speed changing means and with said unloading mechanism in sucha manner that the speed of said compressor is reduced upon an increasein 6. A compressor plant as defined in claim 1 in which said electricmotor driving means includes an electric driving motor operable at onespeed,,a second eleotricdriving motor operable at a different speed,coupling means for selectively coupling said first or second motor tosaid compressor to drive thesame and actuating means for said couplinmeans, said control means being electrically connected to said actuatingmeans.

7. A compressor plant as defined in claim 6 in which said'coupling meanscomprises clutches.

1 JOHN RUTGER MUNCKAF RbSENSCHLD.

pressure above a predetermined value and that I thereof is beingincreased fromone of said speeds to another.

References Cited in the file of this'patent UNITED STATES PATENTS

